EMC spindle speed control

Does EMC have the ability to control the spindle speed in some way?
I notice there are bits on the parallel port definition for spindle
speed decrease/increase, so I assume the answer is yes.

Exactly how they are used and what they represent is what I am
looking for.

I have an AC Tech variable speed drive. It can be controlled via RS-
485. So I was planning on running the EMC control bits through a PIC
so I could translate the EMC commands into the proper RS-485 commands
for the VSD.